1. Field of the Invention
The present invention relates to a starter which starts an engine and, more particularly, to a starter which has a pinion pushing structure and a pinion retreat restricting structure separately for assuring engagement of a pinion gear with an engine ring gear.
2. Description of Related Art
A starter is known as disclosed in Japanese Utility Model Examined Publication No. 51-52647.
This starter is provided with a tube that is fitted on the outer periphery of an armature rotary shaft through a helical spline and a drive ring that is fitted slidably over the outer periphery of this tube. When a pinion gear has meshed with a ring gear, a ball received in the tube fits in a recess formed in an output shaft. The drive ring regulates the outer periphery of this ball and thereby restricts the ball from being drawn off from the recess, whereby it is possible to restrict the retreat of the pinion. On the other hand, after the engine is started, the drive ring moves on and along the outer periphery of the tube and as a result ceases to regulate the ball, with the result that the ball having been regulated is drawn off from the recess due to the centrifugal force to thereby enable the retreat of the pinion gear.
However, in this starter, since a one-way clutch is interposed between the tube receiving the ball therein and the pinion gear, even when the pinion gear is rotated at high speeds by the ring gear after the start of the engine, the rotation of the pinion gear is not transmitted to the tube and the tube is rotated in synchronism with the rotary shaft. That is, since the rotation of the tube is small compared to the rotation of the pinion gear, the centrifugal force that acts on the ball is also small, with the result that the ball becomes unlikely to get off from the recess, whereby insufficient return of the pinion gear occurs.
Another conventional starter is known as disclosed in Japanese Patent Unexamined publication No. 58-178865. In this starter, a pinion gear and a one-way clutch are separated so that only the pinion gear may move along an output shaft. This starter is so constructed that, after the pinion gear is moved to the side end of a ring gear by the operational force (attraction force) of an electromagnet switch, the pinion gear is engaged with the ring gear by the reaction force stored in an engagement biasing spring force. This construction greatly reduces a mass weight of a moving member which is moved by the electromagnet switch and the engagement biasing spring, in comparison with a starter having the construction in which a pinion gear and a one-way clutch are moved together. As a result, the loading to the engagement biasing spring and the attraction force of the electromagnet switch can be reduced, thus advantageously reducing the electromagnet switch in size. Particularly in a reduction type starter in which the rotation of an electric motor is speed-reduced to be transmitted to an output shaft, the loading to an engagement biasing spring can be reduced more greatly because the pinion gear starts to rotate slowly.
In the starter so constructed that the pinion gear and the one-way clutch are separated to move only the pinion along the output shaft, however, pinion gear retreating force will exert on the teeth of helical splines formed respectively on the inner periphery of the pinion gear and the outer periphery of the output shaft when the ring gear rotation speed exceeds the pinion gear rotation speed due to rotation speed variations caused at the time of driving the engine. The loading onto the engagement biasing spring restricts the retreat of the pinion gear. Therefore, with the loading of the engagement biasing spring being smaller than the retreat force exerting on the pinion gear, the engagement of the pinion gear with the engine ring gear is released before the engine starts combustion thus causing misfires.
Even though the loading on the engagement biasing spring can be reduced to reduce the electromagnet switch in size, the reduction in the loading on the engagement biasing spring is limited due to necessity for restricting the retreat of the pinion gear. Thus, great advantage cannot be provided in the reduction in size of the electromagnet switch.